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Understanding speciation and biodiversity patterns in plants requires knowledge of the general role of climate in allowing polyploids to escape competition and persist with their diploid progenitors. This is a particularly interesting issue in widespread species that present multiple ploidy levels and occur across a heterogeneous environment. Chrysolaena (Vernonieae, Asteraceae) is a cytogenetically very diverse genus, with significant interspecific and intraspecific ploidy level variation and with continuous distribution across South America. No previous studies have summarized chromosome count data of Chrysolaena or addressed the cytogeography of the genus. Ploidy level of Chrysolaena species was determined by chromosome counting during mitosis and/or meiosis; the geographic distribution of cytotypes was examined and the correlations between the distribution of particular cytotypes and current ecological conditions were evaluated. A total of 43 new chromosome counts and five ploidy levels (2x, 4x, 6x, 7x, 8x) were reported. The chromosome number of C. cordifolia (2n = 7x = 70) and a new cytotype for C. propinqua var. canescens (2n = 4x = 40) are reported for the first time. Three geographic areas with high diversity of cytotypes and species were detected. The results obtained do not suggest a clear distribution pattern that depends on climatic factors for Chrysolaena populations. However, a geographic pattern was identified in the distribution of ploidy levels, with diploid species presenting a more restricted distribution than polyploid species. [ABSTRACT FROM AUTHOR]

Vegetative anatomical features are poorly known in the South American genus Chrysolaena. In this study, leaves and stems of six Chrysolaena species were described and compared morphologically and anatomically using diaphanization, microtome serial sectioning and scanning electron microscopy. The species differed in leaf epidermis, type of stomata, shape of anticlinal walls of epidermal cells, trichome density, and presence or absence in stems of small air spaces in the cortical parenchyma and of druse-shaped oxalate crystals. Furthermore, glandular trichomes and three types of nonglandular trichomes with different number of basal cells were identified on leaves and stems. Collectively, these features proved instrumental to discriminate among the six studied species, suggesting that leaves and stems of Chrysolaena can represent a source for taxonomically useful characters. We also discuss anatomical features in relation to the environmental conditions in the species' habitats. [ABSTRACT FROM AUTHOR]

Mitotic chromosome numbers of 32 populations belonging to 23 species of the genus Lessingianthus H.Rob. (Vernonieae, Asteraceae) were determined. The chromosome number of all examined plants was found to be based on x = 16. The numbers observed varied from 2 n = 32 to 2 n = 176. The results include the first report of the chromosome number for 11 species: L. lanatus (2 n = 32), L. varroniifolius (2 n = 32), L. cataractarum (2 n = 64), L. intermedius (2 n = 64), L. argenteus (2 n = 96), L. centauropsideus (2 n = 96), L. profusus (2 n = 96), Lessingianthus sp. nov. 1 (2 n = 96), Lessingianthus sp. nov. 2 (2 n = 128), L. robustus (2 n = 160), and L. macrocephalus (2 n = 176). New chromosome numbers were found in the four other species: L. rubricaulis, L. laniferus, and L. sellowii were tetraploid with 2 n = 64, while L. oxyodontus was hexaploid with 2 n = 96. B chromosomes were observed in L. coriaceus and L. varroniifolius. Lessingianthus macrocephalus (2 n = 11 x = 176) is reported as the first case of an odd polyploid and the higher chromosome number of Lessingianthus. The significance of the results is discussed in relation to chromosomal data available for the genus. [ABSTRACT FROM AUTHOR]

Pollen grains from 16 species of Vernonanthura H. Rob. were studied. All the species exhibit the type 'A' pollen characteristic of the genus. These grains are spheroidal to prolate-spheroidal, subechinolophate, tricolporate, with a continuous tectum which is densely microperforate, exhibiting lophae surrounding irregular depressions and having prominent spines. Despite most of the species having a similar pollen type, some taxa can be recognised by the morphology of the spines. According to the spine index (length/width), the species analysed can be divided into three groups having respectively short, medium and long spines. In addition to the size of the spines, some taxa can be distinguished by spine shape. Vernonanthura pinguis (Griseb.) H. Rob. has spines which are constricted at the base, while V. oligactoides (Less.) H. Rob. exhibits small conical spines. Vernonanthura nudiflora (Less.) H. Rob. and V. schulziana (Cabrera) H. Rob. have spines with rounded apices. This study confirms that Vernonanthura is a well-defined group based on pollen characteristics and that pollen morphology is a significant feature in the characterisation of species and genera of Vernonieae. [ABSTRACT FROM AUTHOR]

Centaurium pulchellum is an annual herb native to Europe, but introduced in South America, where it is widely used in the preparation of digestive infusions and bitter drinks. In this species, a wide variation in the aperture pattern of pollen grains was reported and has been attributed to environmental factors or irregularities at meiosis. For this reason, cytological and palynological studies have been undertaken on two different populations. The pollen grain analysis showed that some types are more frequent within each population, but the most common forms were the typical 3-colporate and 4-colporate. The cytological analysis revealed that the analyzed populations of C. pulchellum have chromosome number 2 n = 36. The presence of tetravalents at meiosis strongly suggests that these populations are autotetraploid based on x = 9. The meiotic behavior showed a significant percentage of irregularities in different phases: off-plate bivalents, precocious segregation, laggard chromosomes, bridges, and cytomixis. However these irregularities are not related to the variation in the aperture pattern of pollen grains. The heteromorphism in the pollen grains observed in C. pulchellum could be a normal condition to which the species is well adapted. [ABSTRACT FROM AUTHOR]

The pollen grains of 111 species of Lessingianthus were analysed. Almost all the species belong to the type “B” pollen, characteristic of the genus. These grains are oblate-spheroidal, spheroidal to prolate-spheroidal (P/E 0.93-1.04), echinolophate, 3-colporate, with lacunae in a regular pattern, without polar lacunae. However, some species show variations of this basic type. The type “B-1”, “B-2” and “B-3” grains are respectively 3-porate lacking equatorial lacunae, 3-porate with equatorial lacunae and 3-colporate, psilolophate. Also, one species showed type “D” pollen, a palynomorph present in other genera of the tribe but not reported until now for Lessingianthus. The analysis confirms that the species of the genus constitute well-defined groups based on the pollen characteristics. The results ascertain that pollen morphology is a significant feature in the identification and delimitation of species and genera of Vernonieae. [ABSTRACT FROM AUTHOR]

Two new species of the South American genus Lessingianthus(Asteraceae: Vernonieae) are described and illustrated. One of these species, Lessingianthus arctatus, bears a resemblance to L. linearis(Spreng.) H.Rob. and L. rosmarinifolius(Less.) H.Rob., but can be separated from them by its almost glabrous phyllaries, solitary heads and longer internodes. The other new taxon, Lessingianthus longicuspis, can be easily separated from L. cataractarum(Hieron.) H.Rob. and L. bardanoides(Less.) H.Rob., and other taxa of the genus, by the combination of petiolate leaves, aristate phyllaries and inflorescence bracts alternate to the heads. Four other taxa previously included in Vernoniaare transferred to the genus Lessingianthus. [ABSTRACT FROM AUTHOR]